Sources from the opposition and the regime said the talks would “probably” be face-to-face.

Several rounds of peace talks held by the United Nations have failed to produce a political solution to the conflict.

The Astana talks will assume a different approach, focusing strictly on military developments ahead of political discussions in Switzerland in February.

“The Russian, Turkish and Iranian approach is exactly the opposite of what was previously done in Geneva,” said Waddah Abd Rabbo, editor of the Al Watan daily, which is close to the government.

“The UN thought that if a political solution was reached, it would have an impact on the end of the fighting. But this time, the situation must be resolved on the ground to pave the way for political negotiations,” he said.

Ahmad Ramadan, from the leading National Coalition opposition group, said the Astana talks would aim to reinforce the truce “while the details of the political process will be left to Geneva”.

Osama Abu Zeid, a legal adviser to rebel groups, said rebels were encouraged to attend by the fact that “the agenda will be focused only on the ceasefire” in force since December 30.

The opposition’s delegation to Astana “will be only military” but will consult “a team of legal and political advisers” from the High Negotiations Committee umbrella group, he said.

Abu Zeid said the Jabhat Fateh Al Sham Front, which changed its name from Jabhat Al Nusra after breaking away from Al Qaeda, would not attend the Astana talks.

US President-elect Donald Trump’s transition team has been invited, but has not yet officially responded.

Earlier this month, Syrian President Bashar Al Assad said he was “optimistic” about the talks and would be “ready for reconciliation with [rebels] on the condition that they lay down their arms”.

Syria’s conflict began with protests against Mr Al Assad in 2011, but morphed into a war that has killed 310,000 people and witnessed the rise of extremist groups like ISIL.

The group advanced on Monday around the eastern city of Deir Ezzor, the Syrian Observatory for Human Rights said, cutting off the regime’s access route to a key nearby airport.

“The supply route to the airport is cut, and the city’s eastern half is cut off from its western half,” Observatory head Rami Abdel Rahman said.

A military source said government forces carried out more than 20 air strikes on ISIL positions on Monday.

“ISIL has resorted to heavy use of infiltrators and huge reinforcements from Raqqa and western parts of Deir Ezzor province,” the source said.

Raqqa, to the north, is the de facto capital of the self-styled caliphate ISIL declared across Syria and Iraq more than two years ago.

ISIL already controls more than half of Deir Ezzor and launched a fierce offensive Saturday to capture remaining government-held territory.

The Observatory said the assault has killed at least 28 regime forces so far, as well as 40 ISIL fighters and at least 14 civilians.